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如何在box2d体中设置精灵的位置?

box2d-iphone box2d cocos2d-iphone iphone

Frank · 技术社区 · 16 年前

基本上我的身体有两个多边形。当我为userData添加sprite时,纹理的位置不是我想要的位置。我想做的是调整纹理在身体中的位置。下面是我设置这个的代码示例:

CCSpriteSheet *sheet = (CCSpriteSheet*) [self getChildByTag:kTagSpriteSheet];
CCSprite *pigeonSprite = [CCSprite spriteWithSpriteSheet:sheet rect:CGRectMake(0,0,40,32)];
[sheet addChild:pigeonSprite z:0 tag:kPigeonSprite];

pigeonSprite.position = ccp( p.x, p.y);

bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);
bodyDef.userData = sprite;
b2Body *body = world->CreateBody(&bodyDef);

b2CircleShape dynamicCircle;
dynamicCircle.m_radius = .25f;
dynamicCircle.m_p.Set(0.0f, 1.0f);

        // Define the dynamic body fixture.
b2FixtureDef circleDef;
circleDef.shape = &dynamicCircle;   
circleDef.density = 1.0f;
circleDef.friction = 0.3f;

body->CreateFixture(&circleDef);

b2Vec2 vertices[3];
vertices[0].Set(-0.5f, 0.0f);
vertices[1].Set(0.5f, 0.0f);
vertices[2].Set(0.0f, 1.0f);
b2PolygonShape triangle;
triangle.Set(vertices, 3);

b2FixtureDef triangleDef1;
triangleDef1.shape = &triangle; 
triangleDef1.density = 1.0f;
triangleDef1.friction = 0.3f;

body->CreateFixture(&triangleDef1);

2 回复 | 直到 16 年前

Staffan E 16 年前

我所看到的只是,你在主体的用户数据中存储了一个指向sprite对象的指针,然后把它放在那里。如果你想把身体的位置转移到精灵身上,你需要每帧更新一次。

在C++中,看起来会像这样。

// To be called each time physics should be updated.
void physicsStep(float32 timeStep, int32 velocityIterations, int32 positionIterations) {
    // This is the usual update routine.
    world.Step(timeStep, velocityIterations, positionIterations);
    world.ClearForces();

    // SpriteClass can be replaced with any class you favor.
    // Assume there is a known pointer to the b2Body. Otherwise you'll have to get that,
    // or iterate over all bodies in the world.
    SpriteClass *sprite = (SpriteClass*)body->GetUserData();

    // Once you have the pointer you can transfer all the data.
    sprite.position = body->GetPosition();
    sprite.angle = body->GetAngle();
    // ... and so on
}

用户数据只是b2Body中的任意存储空间,Box2D不知道您决定在那里存储什么。

Singhak 12 年前

要用身体移动精灵,你必须根据身体设置精灵的位置

在你的更新方法中

就像COCOS2D-X中的这个在这里

sprite = static_cast<CCSprite*>body->GetUserData();
sprite->setPosition(vec2(body->GetPosition().x*PTM_RATIO, body->GetPosition().y*PTM_RATIO));
sprite->setRotation(-CC_Radian_to_Degree(body->GetAngle));